1. Field of the Invention
The present invention relates generally to methods, apparatuses, and articles of manufacture for changing a property of a sample, and in particular, for changing a temperature, particle size, and/or chemical composition of a fluidic sample with an opposed migration aerosol classifier (OMAC).
2. Description of the Related Art
(Note: This application references a number of different publications as indicated throughout the specification by reference numbers enclosed in brackets, e.g., [x]. A list of these different publications ordered according to these reference numbers can be found below in the section entitled “References.” Each of these publications is incorporated by reference herein.)
A number of different systems and techniques have been developed for separating and measuring particles contained in fluids such as gases (e.g. aerosols or atmospheric ultrafine particles) and liquids (e.g. colloids or suspensions). Common systems and techniques in the art include the usage of condensation particle counters (CPC) and differential electrical mobility classifiers (DEMC) such as differential mobility analyzers (DMA) and inclined grid mobility analyzers (IGMA). Such systems separate and measure particles according to specific particle properties/characteristics, for example a size, mass or charge of the particle. The systems may also separate and measure particles based on a change in a specific property/characteristic of the particles (e.g. size, mass, charge) when the particles are subjected to certain conditions and environments.
One exemplary application for DMAs in tandem measurements (i.e. tandem differential mobility analysis) is to probe for particle properties such as hygroscopicity and volatility [1, 2]. A typical tandem DMA setup comprises a fixed-voltage DMA that supplies a substantially monodisperse aerosol sample. The temperature and/or vapor composition is then changed, typically by flowing the sample through a denuder or a heated tube. The particles respond to this changed environment, and the extent to which they grow or shrink is determined by using a second DMA operating in scanning mode.
Independent of the system used, oftentimes the greatest difficulty in separating and measuring particles with changing environments is the different time histories of the particles as they traverse the intermediate step where a sample property, such as the temperature or composition, is changed. For example, temperature and vapor changes respectively rely on diffusion from and to the walls of the system, which is often a comparatively slow process relative to the sample flow through the system. Furthermore, particles that are near the walls may experience a substantially different environment as compared to those further away from the walls of the system. Thus, a final measured signal is often an amalgamation of particles subject to inconsistent conditions and environments under a wide range of time histories. Therefore, the effect of changing a property of a sample is difficult to measure and quantify with great certainty and the separation or measurement of specific particles is equally frustrated.
In view of the above, there is a need for a method, apparatus, and article of manufacture for rapidly changing sample properties, such as the fluid temperature, particle size, and/or fluid chemical composition. Furthermore, there is a need for a method, apparatus, and article of manufacture for performing tandem mobility analysis that subjects particles in a sample to uniform conditions and environments under more consistent time histories, which will allow for more easily quantifiable separations and measurements.